Heat oil in a heavy large pot over medium heat. Add leeks and 1/3 cup garlic, sauté until leeks are almost tender but not brown, about 10 minutes. Add stock, potatoes, parsley, thyme and bay leaf. Simmer until potatoes are tender, about 15 minutes. Stir in 1 tablespoon garlic. Season with salt and pepper to taste.

Ladle soup into bowls. Top each with Arugula Pesto, swirl into soup and serve.

Arugula Pesto

4 cups loosely packed arugula leaves (about 2 large bunches)

½ cup freshly grated Parmesan cheese (about 1 ½ ounces)

½ cup extra virgin olive oil

3 tablespoons pine nuts, toasted

2 large garlic cloves, peeled

Blend all ingredients in a food processor until smooth. Season with salt and pepper.